In recent years, a projector has existed which, in order to prevent an illicit use, has a function of carrying out authentication by inputting authentication information such as a code number at the time of use initiation (refer to, for example, Japanese Patent Publication NO. 2000-241874).
The projector disclosed in Japanese Patent Publication NO. 2000-241874 is one which determines whether or not authentication is possible, depending on whether or not a predetermined key operation registered in advance has been carried out after the projector is powered on. According to this, only a user who knows the predetermined key operation can use the projector.
However, the projector disclosed in Japanese Patent Publication NO. 2000-241874 has a problem in that, there also being a case in which the predetermined key operation is learned by a third party, it is impossible to obtain a high level of security. It is also troublesome to carry out the predetermined key operation every time the projector is used, and it may also happen that details of the predetermined key operation are forgotten.